Method and apparatus for removing the crusts of the cooling elements of a continuously operating crystallizer



Oct. 9, 1951 L. vAHL 2,570,612

METHOD AND APPARATUS FOR REMOVING THE CRUSTS OF THE COOLING ELEMENTS OF A CONTINUOUSLY OPERATING CRYSTALLIZER Filed June 1, 1948 Patented Oct. 9, 1951.

METHOD AND- APPARATUS FOR REMOVING THE CRUSTS OF THE COOLING ELEMENTS OF A CONTINUOUSLY CRYS- TALLIZER Laszlo Vahl, Muiderberg, Netherlands, assignor to Werkspoor N. V., Amsterdam, Netherlands, a company of the Netherlands Application June 1, 1948, Serial No. 30,394 In the Netherlands June 5, 1947 4 Claims. (Cl. 23-273) When crystallizing solutions in continuously operating crystallization apparatus the difliculty arises that the crystals form crusts or scale on the surface of the cooling elements which have to be removed. For removing the crusts or scale usually scrapers are provided, scraping the crusts off the cooling surfaces, but with such scrapers the crusts are only incompletely removed and moreover such scrapers are liable to heavy wear particularly with hard crystals.

For removing crusts formed by crystals having a low melting point it has been proposed to melt the crusts periodically by passing hot water or steam instead of the cooling fluid through the cooling elements. Said method, however, has the drawback that the temperature conditions in the continuously operating apparatus are disturbed so that the cleaning of the cooling elements is accompanied by a serious interruption of the normal operation.

The invention has for its object to remove the drawbacks of said known methods and to deal with the formation of crusts or scale on the cooling elements of continuously operating crystallizers in simple manner. According to the invention the crust is periodically molten by'heating means operating on the outer surface of the cooling elements in such a manner that the molten mass flows back into the crystallizing mass. The crystals preferably should have a melting point less than 100 centigrade.

With a crystallizing apparatus comprising cooling elements consisting of a set of rotary hollow discs such as is described in Patent 1,868,406 the heating means for melting the crusts on the discs may be formed as heated scrapers which are periodically brought to their operative position relative to the discs. The heating means may also direct jets of hot air or steam on the.

cooling elements.

The drawing illustrates an embodiment of a device according to the invention as applied to a crystallizing apparatus of the kind described in Patent 1,868,406.

Fig. 1 is a cross section of the crystallization trough and Fig. 2 shows a plan view of a cooling disc and the cooperating heating element formed as a scraper.

In the trough I a rotary hollow shaft 2 is mounted on which sector-shaped cooling discs 3 are secured. With each of said discs 3 a heating element 4 is adapted to cooperate which from time to time is brought into its operative position shown in full lines in Fig. 1. The element 4 which is formed as a scraper is hollow and is heated e. g. by an electric resistance 5 or by steam. The element 4 is normally held in its inoperative position as shown in dotted lines in Fig. 1 and to this end the element l is secured to a shaft 6 in order to be swung by means of lever 1. The heating elements may be actuated automatically or manually.

Whenever the crusts on the cooling discs have grown too thick the element 4 is brought into its operative position and thus acts on the surface of the disc portion extending above the level of the crystallizing mass in order to melt the crusts thereon. During said operation the rotary speed of the discs is preferably reduced. The molten mass flows back into the trough.

Simultaneously with the melting of the crusts on the cooling elements by the heating means the solution to be crystallized may be fed to the surface of the cooling elements whereby the melting and removing of the crusts is facilitated.

What I claim is:

1. A continuously operable crystallization apparatus comprising a container for crystallizing liquid, a plurality of hollow disc-like cooling elements journalled in said container on a substantially horizontal axis for rotative movement through the liquid and with their upper portions above the normal level of the crystallizing mass, and a plurality of scraper members respectively cooperative with said cooling elements and mounted on said container adjacent the upper portions of said cooling elements and for movement between inoperative positions beyond said cooling elements and operative positions adjacent said upper portions of said cooling elements for removing crystallized crusts therefrom.

2. An apparatus as defined in claim 1 wherein said scraper members comprise arms pivotally mounted at one end to extend radially along the sides of said cooling elements when in operative position.

3. An apparatus as defined in claim 1 wherein said scraper members comprise heating means to supply heat from said scraper members to said cooling elements for melting at least a part of the crusts thereon.

4. In a method for removing the crusts from rotary cooling elements of a continuously operating crystallization apparatus for producing crystals having a melting point lower than (7., melting the crusts periodically by externally directing heat on that part of the cooling elements of said apparatus which is above the level of the crystallizing mass, simultaneously scraping the crusts from the cooling elements and returning Number the molten mass to the crystallizing mass. 1,755,059 LAszL VAHL. 1,790,544 1,868,406 REFERENCES CITED 5 2,255,393

The following references are of record in the file of this patent: Number UNITED STATES PATENTS 291,035

Number Name Date 10 1,430,900 Haferkamp Oct. 3, 1922 Name Date Gallagher Apr. 15, 1930 Hoover Jan. 27, 1931 Bonath July 19, 1932 Osborn Sept. 9, 1941 FOREIGN PATENTS Country Date Great Britain Apr. 4, 1929 

1. A CONTINUOUSLY OPERABLE CRYSTALLIZATION APPARATUS COMPRISING A CONTAINER FOR CRYSTALLIZING LIQUID, A PLURALITY OF HOLLOW DISC-LIKE COOLING ELEMENTS JOURNALLED IN SAID CONTAINER ON A SUBSTANTIALLY HORIZONTAL AXIS FOR ROTATIVE MOVEMENT THROUGH THE LIQUID AND WITH THEIR UPPER PORTIONS ABOVE THE NORMAL LEVEL OF THE CRYSTALLIZING MASS, AND A PLURALITY OF SCRAPER MEMBERS RESPECTIVELY COOPERATIVE WITH SAID COOLING ELEMENTS AND MOUNTED ON SAID CONTAINER ADJACENT THE UPPER PORTIONS OF SAID COOLING ELEMENTS AND FOR MOVEMENT BETWEEN INOPERATIVE POSITIONS BEYOND SAID COOLING ELEMENTS AND OPERATIVE POSITIONS ADJA- 